This invention relates to an apparatus for forming a visible image by chromogenic reaction of a colorless dye encapsulated in microcapsules and more particularly to such an image formation apparatus used for a copier or a printer adapted to prevent stains caused by rupture of unnecessary microcapsules.
Japanese Patent Publications Tokkai No. 58-88739 and 59-149343 have disclosed a light and pressure sensitive image formation material composed of a light-accepting sheet having a base sheet coated with microcapsules encapsulating a substance which hardens upon exposure to light and a colorless dye and an image transfer sheet coated with a developer material having chromogenic effects on the colorless dye. To briefly explain the method of image formation by using such a light and pressure sensitive material, an image-forming beam of light reflected, for example, from an original document is made incident on the light-accepting sheet to selectively harden those of the microcapsules exposed to light. If the image transfer sheet is thereafter superposed on the light-accepting sheet and pressed together between rollers, for example, those of the microcapsules not exposed to light and not hardened thereby are ruptured and allow the encapsulated colorless dye to flow out and react chromogenically with the developer material on the image transfer sheet.
When a light-accepting sheet with an invisible image formed thereon by selectively hardened microcapsules and an image transfer sheet superposed and pressed together, however, those microcapsules contacting the external edge areas of the image transfer sheet sometimes rupture and stain the rollers and the like. If the image formation apparatus is of the type which uses light-accepting sheets in the form of a roll, images of sizes A4 and B5, for example, are formed generally as shown in FIG. 4 wherein areas of a light-accepting sheet 3a where no image is formed and where microcapsules are not hardened are hatched for convenience. An image transfer sheet, however, is superposed to cover only an image-carrying area (shown unhatched in FIG. 4) of the light-accepting sheet 3a. Thus, if a roll of light-accepting sheet in a condition as shown in FIG. 4 is compressed between rollers with only the image-carrying area superposed with an image transfer sheet, those of the microcapsules which are in non-image-carrying areas and hence are not hardened rupture, spilling out the encapsulated colorless dye.
If the colorless dye spills on the rollers for compressing the sheets, it may become attached to the back surface of the next image transfer sheet delivered to receive an image. In order to prevent this from happening, a special cleaning device may be required or the apparatus may have to be serviced frequently. Such a cleaning device makes the apparatus complicated and also expensive to manufacture. Requirement of frequent maintenance work, on the other hand, adds burden to the user.